Architecture

Quick answer

• Core APIs: IThumbnailProvider, IInitializeWithStream, IQueryInfo
• Archive layer: Trait-based ZIP/RAR/7z adapters
• Image pipeline: image + fast_image_resize, outputs HBITMAP for Explorer

CBXShell implements modern Windows shell extension interfaces and a trait-based archive layer for ZIP, RAR, and 7z formats.

COM implementation

• IThumbnailProvider for thumbnail extraction
• IInitializeWithStream for stream-based archive access
• IQueryInfo for tooltip metadata

Legacy interfaces are retained for compatibility:

• IPersistFile
• IExtractImage2

Archive support

The archive layer exposes a unified trait API:

pub trait Archive: Send {
    fn find_first_image(&mut self, sort: bool) -> Result<ArchiveEntry>;
    fn extract_to_memory(&mut self, entry: &ArchiveEntry) -> Result<Vec<u8>>;
    fn get_info(&self) -> Result<ArchiveInfo>;
}

Implementations:

• Zip: zip crate
• Rar: unrar crate
• 7z: sevenz-rust crate

Image processing

• Hybrid decode pipeline:
  • Primary: Windows WIC decoder (uses OS codecs, optional modern codec support)
  • Fallback: Rust image crate decoder
• WebP, AVIF, JPEG, PNG, GIF, BMP, TIFF, ICO (availability depends on OS codec installation for WIC path)
• High-quality resize via fast_image_resize (Lanczos3)
• HBITMAP generation for Explorer integration

Why WIC-first?

• Keeps binary size smaller compared to bundling full external codec stacks.
• Lets CBXShell benefit from platform codec updates (for example AVIF support through installed Windows codecs).
• Maintains compatibility through automatic fallback when WIC decode is unavailable or fails.